The present invention relates to vehicle instrumentation including speedometers and tachometers, and in particular to a display system allowing for the smooth display of changing but irregularly transmitted data.
Driver display data that was once transmitted as analog voltages (e.g., fuel level) or mechanically (e.g., road speed) is now transmitted as digital words in serial fashion on a digital communications network within the vehicle. The digital words representing data from different sources may be interleaved to be transmitted on a single cable ("time multiplexed") thereby substantially reducing wiring weight and costs. Display devices may be attached to this network to receive and display data related to their function. Such displays may include those providing numeric outputs ("digital displays") or those having a moving pointer ("analog displays").
Efficiencies in circuitry may be obtained if several vehicle sensors communicate with a single network interface card. The interface card converts data from the sensors to the proper format for transmission on the network and handles the necessary network protocols.
Often a network interface card will process both engine control data such as that from oxygen, air mass and fuel flow sensors, as well as driver display information from speedometer and tachometer senders. During certain times of rapidly changing engine conditions, such as during acceleration, the transmission of higher priority engine control data may interfere with the regular transmission of driver display information. This can result in a "stepping" or jerkiness in the operations of displays such as the speedometer or tachometer, which are also receiving rapidly changing data.